It is known that there are valuable residual reserves of natural gas that are not economically recoverable with primary production techniques. Although there has been considerable attention paid to the development and implementation of both secondary and tertiary enhanced oil recovery (“EOR”) processes over the last half century, there has been comparatively little attention given to the potential for enhanced natural gas recovery (“EGR”) processes. This may be due in part to the fact that conventional oil reservoirs will typically produce only 10–30% of their original oil in place under primary recovery, while most conventional natural gas reservoirs will produce 60–90% of their original gas in place through natural reservoir pressure depletion.
One of the EGR processes that has received considerable attention in technical publications is the process of injecting an inert gas such as carbon dioxide or nitrogen into a conventional natural gas reservoir for purposes of displacing residual natural gas away from injection wells and toward production wells, with the expectation that such process will result in an increase in the total quantity of natural gas ultimately recovered from the reservoir (“Gas Displacement EGR”). However, the relatively high cost of producing and injecting a concentrated or near-purity stream of either carbon dioxide or nitrogen has been a factor that has inhibited the commercial adoption of Gas Displacement EGR using those gases.
Recent developments in the field suggest that flue gas and other gaseous effluent emitted from any of a range of industrial facilities could provide a more cost effective displacement agent for Gas Displacement EGR. Such effluent (“Waste Gas”) may contain any one or more of carbon dioxide, nitrogen, oxygen, sulphur dioxide, nitrous oxide, nitrogen dioxide and other substances. “Waste Gas EGR” is described as a process for increasing the quantities of methane and associated hydrocarbon gases (“natural gas”), and in some instances associated hydrocarbon liquids, recoverable from a subterranean reservoir, through the controlled injection of Waste Gas into that reservoir. The basic principle underlying the Waste Gas EGR process is that the injection of Waste Gas into the reservoir through one or more injection wells will both increase reservoir pressure outward from those wells and displace residual natural gas towards wells that continue to be used for production, resulting in an increase in the amount of remaining natural gas that is ultimately recovered from the reservoir.
Because the pressure pulse resulting from Waste Gas injection will spread through the reservoir much more quickly than will the Waste Gas itself, increases in natural gas production can be expected to occur at points quite distant from the Waste Gas flood front, meaning that production wells will generally begin to experience increased natural gas production rates well before injected Waste Gas reaches them (FIG. 1). Factors such as reservoir permeability, heterogeneity, size and dimensions, as well as the presence and influence of water and the stage of primary depletion production, will all have a bearing on the effectiveness and efficiency of Waste Gas EGR in any particular reservoir situation.
The primary components of a Waste Gas stream will generally be nitrogen, carbon dioxide and, in some cases, oxygen. The density and viscosity characteristics of these substances relative to those of methane make them advantageous agents for displacing or sweeping natural gas towards production wells (Table 1). Because all of the primary Waste Gas components are more viscous than methane under reservoir conditions, they will flow through the porous media constituting the reservoir less readily than will methane, thus tending to push methane ahead of them as they move through the reservoir. The primary Waste Gas components also all have higher densities (i.e., gravity) than methane, meaning that they will generally tend to remain or gravitate lower in the reservoir than methane. If injected in the lower regions of a reservoir they will accordingly tend to displace methane upwards towards the upper regions of the reservoir. The combination of these factors means that, even though all of the primary Waste Gas components are miscible with methane under reservoir conditions, Waste Gas injected into a select region of the reservoir at an appropriate pressure and rate will tend to mix with the methane in the reservoir only for a limited distance past the initial point of contact, creating a well defined fluid interface or flood front of mixed Waste Gas and methane that will push methane ahead of it as Waste Gas continues to enter the reservoir behind it (FIG. 2). Although reservoir heterogeneity will affect the uniformity of this flood front, the “fingering” or “streaking” complications that have been encountered in gas-based EOR schemes will not be as significant an issue in Waste Gas EGR because the displacement agent is more viscous, as opposed to less viscous, than the hydrocarbon being displaced. Depending on reservoir constituents, the relative solubility and reactivity of the Waste Gas components may also be significant factors in Waste Gas EGR performance.
In most instances the raw Waste Gas stream will have to be treated to remove water and any other potentially problematic substances that may be present, but as a general rule the treatment required to render Waste Gas suitable for use as a displacement agent will be much less expensive than the processing required to produce a relatively pure stream of either carbon dioxide or nitrogen from Waste Gas.
Some publications of relevance to waste gas EGR include:
Stinson, D. L., “Secondary Recovery of Natural Gas”, Society of Petroleum Engineers Paper No. SPE 1240, presented at the October, 1965 SPE Annual Fall Meeting in Denver, Colo.
U.S. Pat. No. 4,393,936 filed Sep. 21, 1981 on behalf of Virgil A. Josendal (Inventor) and Union Oil Company of California (Assignee), granted in 1983.
Zotov, G. A.; Pestryakov, A. K.; Sokolov, V. A., “The Primary Principles of Determining the Optimum Constant Recovery Periods from Gas Fields”, Russian Analytical Book published 1983.
Duckett, M; Banks, R; Limb, D, “Using Nitrogen to Enhance Oil and Gas Recovery”, Journal World Oil, articled in July, 1983.
Clancy, J. P; Bywater, D. R.; Cheng, L. H. K.; Gilchrist, R. E., “Analysis of Nitrogen-injection Projects to Develop Screening Guides and Offshore Design Criteria”, Journal J. Pet. Technol, articled in June, 1985.
Carriére, J. F.; Fasanino, G; Tek, M. R., “Mixing in Underground Storage Reservoirs”, Society of Petroleum Engineers Paper No SPE-14202, 9–12, presented at September, 1985, 60th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers in Las Vegas, Nev.
Laille, J. P.; Molinard, J. E.; Wents, A., “Inert Gas Injection as Part of the Cushion of the Underground Storage of Saint-Clair-Sur-Epte, France”, Society of Petroleum Engineers Paper No. SPE-17740, 343–352, presented at June, 1988, SPE Gasa Technology Symposium in Dallas, Tex.
van der Burgt, M. J.; Cantle, J; Boutkan, V. K., “Carbon Dioxide disposal from coal-based IGCCs in depleted gas fields. In: Proceedings of the First International Conference on Carbon Dioxide Removal”, Energy Conversion & Management, 1992, 33 (5–8), 603–610.
Kokal, S; Sayegh, S, “Enhanced Gas Recovery: Prospects and Technology”, Analytical report presented at the May, 1993-44th Annual meeting of the Petroleum Society of Canadian Institute of Mining and Metallurgy (CIM) in Calgary, Alberta.
Norwegian Patent No. NO 173146/B/, filed Nov. 7, 1984 on behalf of Andreasson, E. M.; Egeli, F; Holmberg, K. A.; Nystroem, B; Stridh, K. G.; Oesterberg, E. M. (Inventors) and Berol Kemi A B, Stenungsund (Sweden); Tendex Kjemiservice A/S Stavanger (Norway) (Assignees), granted Jul. 26, 1993.
Dindoruk, B; Orr, F. M. Jr.; Johns, R. T., “Theory of Multicontact Miscible Displacement with Nitrogen”, Analytical Book presented at the October, 1995—Annual meeting of the Society of Petroleum Engineers (SPE) in Dallas, Tex.
Blok, K; Williams, R. H.; Katofsky, R. E.; Hendriks, C. A., “Hydrogen Production from Natural Gas Sequestration of Recovered CO2 in Depleted Gas Wells and Enhanced Natural Gas Recovery”, Energy: The International Journal, 1997, 22 (2–3), 161–168.
Papay, Jozsef, “Improved Recovery of Conventional Natural Gas, Part 1: Theoretical Discussion of Recovery Methods”, Journal Erdoel Erdgas Kohle, June, 1999, and “Improved Recovery of Conventional Natural Gas. Part. 2; Results of a Pilot Test”, Journal Erdoel Erdgas Kohle, July/August 1999.
Oldenburg, C M; Pruess, K; Benson, S. M; (E. O. Lawrence Berkeley National Laboratory), “Process Modeling of CO2 Injection into Natural Gas Reservoirs for Carbon Sequestration and Enhanced Gas Recovery”, Journal of Energy and Fuels, Vol. 15 Mar–April, 2001, presented at the August, 2000 American Chemical Society Division of Fuel Chemistry Symposium on CO2 Capture in Washington, D.C.
Oldenburg, C M; Benson, S M; (E. O. Lawrence Berkeley National Laboratory), “Carbon Sequestration with Enhanced Gas Recovery: Identifying Candidate Sites for Pilot Study”, (2002)
Oldenburg, C. M. and Benson, S. M., “CO2 Injection for Enhanced Gas Production and Carbon Sequestration”, SPE 74367, presented at the February, 2002 SPE International Petroleum Conference.
Mamora, D. D. and Seo, J. G., “Enhanced Gas Recovery by Carbon Dioxide Sequestration in Depleted Gas Reservoirs”, SPE 77347, presented at the October, 2002 SPE Annual Technical Conference, San Antonia, Tex.
Clemens, Torsten and Wit, Krijn, “CO2 Enhanced Gas Recovery Studied for an Example Gas Reservoir”, SPE 77348, presented at the October, 2002 SPE Annual Technical Conference in San Antonio, Tex.
Oldenburg, C M; Stevens, S H; Benson Steve Mulherin. “Economic Feasibility of Carbon Sequestration with Enhanced Gas Recovery (SCSEGR)” Lawrence Berkely National Laboratory, Berkely, Calif. 2003 Ross, Elsie “Carbon Dioxide has Milt-Role Potential in Gas Reservoirs” New Technology Magazine, April/May 2003.
To Applicant's knowledge, the general Waste Gas EGR concept is not currently in use and is not widely recognized as viable, although the concept has been the subject of academic consideration. Some publications providing additional technical background in this respect, the entirety of which are incorporated herein by reference, are listed in Appendix A.